The symbols or numbers disposed on the hour-circle, or on secondary dials, are usually made by transferring, or by screen printing, giving the impression that they are printed. These symbols can also be obtained by dying the lower surface of the dial, the parts in relief forming the symbols then being polished, varnished or covered with a luminescent pigment, as described for example in FR Patent No. 2 308 133. These symbols can also be parts added to the dial being produced by stamping a metal plate, then by bonding, for example using a hot setting adhesive, as indicated in CH Patent No. 506 111.
When one wishes to obtain high quality pieces, in particular when the metal used is a precious metal, the symbols, which are then usually provided with feet for securing them to the dial by driving them into housings provided for such purpose, are roughed out by machining or stamping a profile, then taken to be faceted. The sections employed are generally rectangular, either along a “longitudinal” mode, or along a “transverse” mode.
According to the first embodiment, the profile has a section in which a cross section of a symbol, including the feet, can be inscribed. Over a certain profile length corresponding to several symbols placed end-to-end, a face is first machined to form the definitive appearance of the visible part of the symbols, then the feet are formed by milling the opposite face. The symbols are then cut off and fall into a tank for the subsequent cleaning and drying operations before being packed in bulk for dispatch. One embodiment of this type is described in more detail for example in U.S. Pat. No. 3,323,396. This method has the drawback of not allowing the cut off part to be finished, for example by diamondpolishing. There also exists a risk of the feet, which are very fine little rods with a diameter of less than a millimeter, being damaged when dropped into the container, which can lead to a discard rate of 30% or even more.
According to a second embodiment, the profile has a section in which the contour selected for the base of a symbol can be inscribed. In a first operation, the upper faces and sides of the symbols are diamondpolished. In a second operation, the symbol is gripped on two opposite support surfaces between the jaws of a hard metal clamp to be cut along a length substantially corresponding to the thickness of the symbol, increased by the height of the feet. In a third operation, the feet are milled, then the symbols are released and they drop into a tank for the subsequent bulk cleaning and drying operations, before being packed. According to a variant of this embodiment, disclosed in CH Patent No. 565 406, the end of the profile is gripped by a clamp over a length corresponding to the length of the feet, then a section is cut off and brought by a revolving table before a faceting station, then before a turret where it is picked up by another clamp on opposite sides that have already been faceted, in order to the two feet to be milled in succession. As can be seen, in this embodiment, in which finished surfaces are gripped between clamps in order to execute the final machining of the feet, there is a high risk of producing symbols with visible defects in appearance causing them to be downgraded or even rejected when said symbols are intended for top of the range timepieces.